Jianhu Zhao

Study on underwater navigation system based on geomagnetic match technique

Underwater vehicle navigation technique is one of the important issues to the development and application of the long-range underwater vehicle technology. In order to meet the concealment of underwater navigation, we present a kind of independent underwater navigation system based on geomagnetic match technique in this paper. Firstly, we introduce the composition of the system, the work principles and functions of each component. In the whole system, the navigation algorithm is the core. Therefore, we study two match navigation algorithms, which are the terrain contour matching (TERCOM) and the iterated closest contour point (ICCP). Based on above researches, we design the system of underwater geomagnetic navigation. The system is tested and proved by actual experiments. The results show that the system of underwater geomagnetic matching navigation is accurate and credible. Some suggestions are also given finally.

Study on key technologies of construction of marine geomagnetic filed model based on polynomial method

There is an important relationship between the research of geomagnetic field model and the digital earth. The earth information includes that of geomagnetic field. Geomagnetic field model is to describe the geomagnetic field in mathematic way. It can provide the precise geomagnetic field information to help the development of the digital earth. At the same time, the geomagnetic field model is also used in the land and underwater geomagnetic navigation, and acts as an important role in finding underwater targets. Thus the paper will focus the research how to build a local marine geomagnetic field model. Firstly, we use the polynomial model, which includes Taylor polynomial model and Legendre polynomial model, to build the local marine geomagnetic model. Because geomagnetic field model expresses the steady geomagnetic change of the earth core. Thus we study Robust Kalman filter to eliminate the influences of abnormal geomagnetic data secondly. Besides, we also study the determination of model truncation order in using polynomial modeling, Because model truncation determines model accuracy and the efficiency in building local marine geomagnetic model. Model accuracy can be estimated by the standard deviation in interior test and exterior test. In the research, we find that model accuracy changes with model order, when the accuracy become stability with model order, we regard the order as model truncation order. Using above conclusions, we implement a experiment in the situations of geomagnetism mild change and geomagnetism complex change. We find that both Taylor polynomial model and Legendre polynomial model have smaller model truncation order in the situations of geomagnetism mild change than that in the situations of geomagnetism complex change. We also compare and analyze Taylor polynomial modeling and Legendre polynomial modeling in a large water area. By comparing and analysis, we find that Taylor polynomial modeling has higher accuracy and faster convergence speed than Legendre polynomial molding. Thus Taylor polynomial is recommended as a optimum polynomial method in building local marine geomagnetic model. Finally we use both Taylor polynomial method and Legendre polynomial method to construct the local geomagnetic field model in the experimental water area of Bohai Bay in China. Taylor polynomial model achieves lower model truncation order and satisfying accuracy relative to Legendre polynomial model, which further prove above conclusions.

A New Radiometric Correction Method for Side-Scan Sonar Images in Consideration of Seabed Sediment Variation

Affected by the residual of time varying gain, beam patterns, angular responses, and sonar altitude variations, radiometric distortion degrades the quality of side-scan sonar images and seriously affects the application of these images. However, existing methods cannot correct distortion effectively, especially in the presence of seabed sediment variation. This study proposes a new radiometric correction method for side-scan sonar images that considers seabed sediment variation. First, the different effects on backscatter strength (BS) are analyzed, and along-track distortion is removed by establishing a linear relationship between distortion and sonar altitude. Second, because the angle-related effects on BSs with the same incident angle are the same, a novel method of unsupervised sediment classification is proposed for side-scan sonar images. Finally, the angle–BS curves of different sediments are obtained, and angle-related radiometric distortion is corrected. Experiments prove the validity of the proposed method.

A Study of Underwater Terrain Navigation based on the Robust Matching Method

Outliers in terrain data are an obstacle to achieving accurate and robust solutions of Underwater Terrain Relative Navigation (UTRN). If not handled properly, navigation may be degraded or even divergent. To address the problem, this paper proposes a terrain-matching algorithm based on the robust estimation theory. In contrast to the conventional approach, the proposed algorithm can significantly reduce the interference of the outliers. Experimental results confirm the good performance of the proposed method.

Mosaic method of side-scan sonar strip images using corresponding features

The towing operation mode of side-scan sonar system (SSS) easily results in dislocations and distortions of targets in the SSS strip image, brings difficulty to the mosaic of these strip images by the geocoding method or the tessellation-line method and affects the recognition and understanding for seabed relief. Therefore this study proposes a new method, namely the segment-image mosaic method based on corresponding features of the two adjacent SSS strip images. Through SSS image preprocessing, segment match based on corresponding features and image fusion in the common coverage area based on wavelet transformation, this new method overcomes the drawbacks of the traditional methods of image mosaic, fulfils well the mosaic of SSS strip images and finally a whole-area SSS image is formed. Experiments have verified that the mosaic image formed by the new method can correctly reflect the position, shape and distribution of seabed targets, which is helpful to understand seabed relief.

Shallow Water Measurements Using a Single Green Laser Corrected by Building a Near Water Surface Penetration Model

To reduce the size and cost of an integrated infrared (IR) and green airborne LiDAR bathymetry (ALB) system, and improve the accuracy of the green ALB system, this study proposes a method to accurately determine water surface and water bottom heights using a single green laser corrected by the near water surface penetration (NWSP) model. The factors that influence the NWSP of green laser are likewise analyzed. In addition, an NWSP modeling method is proposed to determine the relationship between NWSP and the suspended sediment concentration (SSC) of the surface layer, scanning angle of a laser beam and sensor height. The water surface and water bottom height models are deduced by considering NWSP and using only green laser based on the measurement principle of the IR laser and green laser, as well as employing the relationship between NWSP and the time delay of the surface return of the green laser. Lastly, these methods and models are applied to a practical ALB measurement. Standard deviations of 3.0, 5.3, and 1.3 cm are obtained by the NWSP, water-surface height, and water-bottom height models, respectively. Several beneficial conclusions and recommendations are drawn through the experiments and discussions.

Side scan sonar image segmentation based on neutrosophic set and quantum-behaved particle swarm optimization algorithm

To fulfill side scan sonar (SSS) image segmentation accurately and efficiently, a novel segmentation algorithm based on neutrosophic set (NS) and quantum-behaved particle swarm optimization (QPSO) is proposed in this paper. Firstly, the neutrosophic subset images are obtained by transforming the input image into the NS domain. Then, a co-occurrence matrix is accurately constructed based on these subset images, and the entropy of the gray level image is described to serve as the fitness function of the QPSO algorithm. Moreover, the optimal two-dimensional segmentation threshold vector is quickly obtained by QPSO. Finally, the contours of the interested target are segmented with the threshold vector and extracted by the mathematic morphology operation. To further improve the segmentation efficiency, the single threshold segmentation, an alternative algorithm, is recommended for the shadow segmentation by considering the gray level characteristics of the shadow. The accuracy and efficiency of the proposed algorithm are assessed with experiments of SSS image segmentation.

Study on side scan sonar image matching based on the integration of SURF and similarity calculation of typical areas

In this paper, a method for side scan sonar image matching is proposed based on SURF and similarity calculating in typical areas. The process is composed of three steps of rough matching, geometric correction and accurate matching. Firstly, rough matching is implemented to get a rough matching relationship of reference image and matching image based on SURF. Then geometric correction is executed with the relationship to make the matching image have a same viewing condition with the reference image. Finally, accurate matching is implemented by similarity calculating of typical areas in two corrected images. This matching algorithm combined the merits of the regional matching and feature matching. Experiment proved that the method has advantages in speed, accuracy, reliability and invariance to geometric differences between two side scan sonar images.

Improving instantaneous height quality of transducer in precise bathymetric measurement based on multi-information fusion

Tide-independent precise underwater topographic surveying technique is widely used in inshore hydrographic measurement. GPS RTK provides an accurate instantaneous height to transducer in the technique. However the instantaneous height easily suffers the influences of satellite status, vessel attitude and radio transmission and so on and becomes weak in quality. The low-quality instantaneous height influences seriously the accuracy of vertical solution in final underwater topographic result. Thus it is necessary to study quality control of the instantaneous height. Kalman filter is valid for filtering a small quantity of abnormal height records. However it brings easily filtering radiation when continuous or large quantity of abnormal height records appear in the instantaneous height series. In order to ensure the accuracy of tide-independent underwater topographic measurement, A new method, which based on multi-information fusion, is studied for improving the instantaneous height quality of transducer in the paper.

Underwater Navigation Based on Real-Time Simultaneous Sound Speed Profile Correction

Abstract Precise sound speed profile (SSP) information is critical when using sonar for underwater terrain navigation. Nevertheless, acquiring SSP information in real-time is difficult, especially in underwater navigation environment. To account for this problem, this paper presents an underwater navigation method that applies real-time SSP correction to the terrain measurements. The method uses a probe to measure the surface sound speed simultaneously. Meanwhile, redundancy of topographic measurement data is exploited to derive the equivalent SSP information. The acquired equivalent SSP is updated continuously with particle filter algorithm. The terrain measurements can be corrected in real-time with the equivalent SSP to improve the performance of underwater terrain navigation. By removing the impact of inaccurate SSP from the terrain measurements, the proposed method can achieve precise and robust underwater navigation result without using an underway-profiling instrument. Simulated results confirm the good performance of the proposed method.